Long-term mental illnesses such as schizophrenia or affective disorders often impose a burden on the patients who suffer from it, as well as on their carers (relatives or friends). There are many instruments measuring family or caregiver burden. One of these instruments is the Involvement Evaluation Questionnaire (IEQ). The IEQ is a 31-item questionnaire which is completed by the caregiver. The IEQ contains 27 items that can be divided into four subscales (domains): tension (nine items), worrying (six items), supervision (six items) and urging (eight items). Two items appear in more than one domain. The items are scored on a 5-point Likert scale (never, sometimes, regularly, often and always). There is no full Polish adaptation of IEQ so far. The psychometric properties of the IEQ and its culture-profiled versions are satisfying and comparable. The IEQ, as a self-assessment instrument, is easy to administer and not time-consuming. The IEQ proved to be a reliable instrument for measuring caregiver consequences in mental healthcare.